Thermally-induced transformation of hexabromocyclo dodecanes and isobutoxypenta bromocyclododecanes in flame-proofed polystyrene materials

Polystyrenes (PS) are produced in quantities exceeding 10 Mt y−1. They are used for insulation and packaging materials, often in flame-proofed forms with hexabromocyclododecanes (HBCDs) added as flame retardants. Polystyrenes are also constituents of plastic debris found in the aquatic environment. HBCDs are now considered as persistent, bioaccumulative, and toxic compounds. Lately, we reported that isobutoxypenta bromocyclododecanes (iBPBCDs), a formerly unknown class of polybrominated compounds, are also present in flame-proofed polystyrenes. It is therefore likely that iBPBCDs are released along with HBCDs from these materials. Herein, we report on changes of the HBCD- and iBPBCD-patterns when exposing expanded (EPS) and extruded (XPS) polystyrenes at temperatures of 140–160 °C. Substantial transformation reactions were observed in EPS, which was rich in γ-HBCDs and δ-, η-, and θ-iBPBCDs at the beginning, but changed to materials rich in α-HBCDs and α-, β-, ε-, and ξ-iBPBCDs. Patterns of untreated XPS already resembled those of the thermally treated EPS. Upon thermal exposure, some further enrichment of α-HBCDs and α-, β-, ε-, and ξ-iBPBCDs was also noticed for the XPS samples, indicating similar transformation mechanisms. Comparable apparent first-order transformation rate constants (ktrans) of −0.003, −0.008, and −0.020 min−1 and −0.004, −0.009, and −0.019 min−1 are found for γ-HBCD- and δ-iBPBCD-conversion at 140, 150, and 160 °C, respectively. We conclude that a thermal treatment of flame-proofed polystyrenes alters their HBCD- and iBPBCD-patterns. Thus depending on the proportions of EPS and XPS materials reaching the environment, more of the lipophilic (late-eluting) or of the more polar (early-eluting) HBCD- and iBPBCD-stereoisomers will be released. Several properties such as partitioning coefficients, degradation rates, and bioaccumulation factors are stereoisomer-specific. Therefore, the environmental fate of individual HBCDs and iBPBCDs is expected to vary, the specific stereoisomer pattern in polystyrenes at a potential source is another important aspect to consider.